Two conductive metal plates are stacked and bonded by resistance-welding so as to connect circuits of an electronic device. A current is applied for the resistance-welding of metal plates while a pressure is applied by sandwiching both sides of the stacked metal plates with electrodes, so as to bond the metal plates by spot welding performed by generated resistance heat.
In order to reduce power consumption by the electronic device, a conductive copper material is used for a conductor, such as a bus bar, for connecting circuits. The resistance of copper material is small, and can hardly generate resistance heat on spot welding. Accordingly, a projection is provided on a conductor, and a tip of this projection is attached to a welding part of the other conductor and then a current is applied in embossing projection welding, so as to concentrate a current on the tip of projection to generate resistance heat for bonding two conductors.
PTL1 discloses a technique achieving good welding condition without collapsing a tip of a projection and biting into the other bus bar on welding by providing a smoothly-curved projection on one conductor.